This invention is directed to a liquid crystal display device and, in particular, to a liquid crystal display device wherein data may be written on a liquid crystal panel of the display device by means of a "light pen" which can be used for entering data in a data processor or the like.
In luster scanning type display devices, a light pen is provided for specifying particular points on the display area by means of comparing the output of a sensor in the light pen which includes a light receiving element with the scanning time of the display device. Such display devices, when use with a light pen, has been quite effective for inputting data to a processor.
However, with respect to a liquid crystal display device as compared with a cathode ray tube (CRT) display device, the response speed of the liquid crystal display device is much slower than that of the CRT. Moreover, the known methods of driving a liquid crystal display device are different from that of the driving method for the CRT. In the CRT display device, one frame is formed by gradually scanning the display area. However, liquid crystal display devices were not driven in this manner and were not provided with a light pen function for inputting data. See U.S. Pat. No. 3,967,253, for example.
A liquid crystal display which can be used for inputting data to a data processing machines or the like would have a great benefit in that the liquid crystal display has a low power consumption and a thin size. In recent years, the application of the liquid crystal display panel has developed from a seven-segment type display for forming several digits to a dot matrix display which defines a plurality of dots which form characters or digits. As a result, it is now possible to display a plurality of letters and digits as well as a graphic display on a liquid crystal display device. Accordingly, a liquid crystal display device wherein data can be input thereto by means of a light pen, is desired.